1. Field of the Invention
This invention relates to a magnetic memory device of the type employed with electronic data processing equipment. More particularly this invention relates to means and a method for compensating a magnetic memory device against interruptions caused by external shock forces.
Heretofore, magnetic memory devices such as a disk file system or a drum system have been mounted on shock absorbers and resilient supports in order to damp out shock vibrations. The shock absorbers of the prior art type have been found to provide sufficient damping to avoid interruptions and malfunctions in most industrial applications where shock forces up to several times the force of gravity have been encountered.
When an externally applied shock force exceeds thirty times the force of gravity the ability of a well-built shock absorber to protect the drum or disk magnetic memory device becomes questionable. If a shock force is applied repeatedly or periodically to a system the shock forces build up due to resonant vibration.
2. Description of the Prior Art
Heretofore, prior art rotatable magnetic storage devices were not provided with impact shock compensating systems.
Prior art magnetic storage devices are known to be mounted on shock absorbing means to reduce and attenuate impact shock forces. Shock absorbers do not compensate for impact shock forces, but merely reduce the force transmitted through the shock absorber.
When a magnetic storage device is disturbed by impact forces sufficient to cause the gap or space between the flying head and the magnetic device to change, the head may crash into the magnetic device causing permanent damage to the magnetic medium and/or the flying head. Often such damage results in the destruction of information stored in the magnetic media and/or can destroy the usefulness of the magnetic storage device.
When a disturbance causes a magnetic head to move away from the magnetic media during active operation, information may not be properly written in or read out of the magnetic media. The usefulness of the magnetic storage system may be interrupted to the extent as to cause a subsequent malfunction or error.
To minimize the damage caused by flying heads crashing into a rotating magnetic media, protective plastic coatings have been applied over the magnetic media to protect the magnetic coating. Some prior art magnetic media comprises a homogeneous tough plastic impregnated with magnetic particles. While such homogeneous magnetic media offers some protection against heads which crash into the plastic they do not permit the more advanced flying heads to generate high density recording data.
U.S. Pat. No. 3,913,138 shows and describes a flying magnetic head capable of flying about ten to twenty microinches above a magnetic disk. Such a low flying heads are most prone to crash because the layer between the head and the disk has been reduced to a minimum. When the externally applied shock impact forces are sufficient to create undulations in the rotating disk the gap between the head and the disk is both increased and decreased during a single revolution of the disk and the chances of a crash occurring are increased.
Prior art flying heads which have a high mass are usually biased downward by spring pressure toward the magnetic media to cause the head to fly in the laminar layer of air on the surface of the disk. High mass heads cannot be maintained at the same gap distance above a disk when the impact force causes an undulation of the disk which exceeds the gap distance.